A common concern in golf club manufacturing is maximizing the ability to position mass in a desired location within a club head while maintaining the club head's structural integrity. A target mass is often selected corresponding to the desired total mass of a finished club head. The target mass may be a function of the expected maximum length of a shaft that may be assembled to the head and the selection of grips that may be fitted thereto. A minimum structural mass of a club head corresponds to the minimum mass of all structural components required to produce a club head having a desired shape that can withstand typical loads applied to the club head during use. The difference between the target mass and the minimum structural mass, i.e. discretionary mass, is often sought to be maximized.
Placement of discretionary mass is known to affect characteristics associated with the performance of the club head. For example, such placement affects the location of the center of gravity of the club head. Also, the location of discretionary mass about a club head affects the orientation of the principal axes of inertia passing through the center of gravity, and the moments and products of inertia about them.
Regarding the location of the center of gravity, it is known that a low (close to the bottom portion, or sole, of the club head) and deep (rearward from the face center of the striking face of the club head) center of gravity provides beneficial launch conditions at the moment of impact with a golf ball. Specifically, a low center of gravity increases launch angle and decreases ball spin, which increases carry and overall distance. A deeper center of gravity reduces backspin imparted to the golf ball at impact.
Because of golfers' increasing desire for club heads of larger volume, the concern for maximizing discretionary mass and optimizing its position is more significant. For example, increasing head volume while maintaining a traditional head shape reduces weight budget and, thus, the ability to improve performance of the club head.
Some attempts have been made to mitigate these concerns, but with mixed results. Golf club manufacturers have adapted thin-walled casting techniques for metal wood head portions such as the crown, sole, or skirt. Also, manufacturers have increasingly opted for materials having a specific strength (ultimate tensile strength divided by specific gravity) that is greater than conventional head materials such as steel or titanium, for certain portions of the club head. However, these types of club heads are generally expensive to manufacture. Further, the acoustic properties of these club heads have been compromised. In addition, manufacturers have applied composite materials, e.g., carbon fiber reinforced epoxy or carbon fiber reinforced polymer, to form portions of the head. However, such heads have suffered from durability, performance, and manufacturing issues generally associated with composite materials.